The field of the invention is glow plugs and the invention relates more particularly to a high performance glow plug for use in state of the art engines, particularly in model car engines.
Internal combustion model cars have been refined to an extent that tethered model cars can substantially exceed 200 mph. In such extreme environments the glow plugs are heated to a temperature where conventional glow plugs will leak and fail. Various improvements in glow plug construction have been made. One such improvement is shown in U.S. Pat. No. 6,346,688 having the same applicant as the present application. This patent is incorporated by reference herein.
Temperatures at the lower end of a glow plug can reach in excess of 1000xc2x0 F. The combination of the pressure in the cylinder of the engine and the high temperature of the lower end of the glow plug can result in the formation of leaks which reduce the compression within the cylinder which is highly detrimental to the performance of the engine. Various attempts at improving the crimping at the top of the glow plug have reduced, but not eliminated, the problem.
It is an object of the present invention to provide a glow plug which can withstand state of the art high performance temperatures and pressures without leaking.
The present invention is for a glow plug having a body which can be affixed to an engine block and has an outer shell surrounding an inner cavity. The inner cavity of the body has a frusto-conical sidewall portion extending upwardly to a pressure-applying portion of the body. An inner electrode is held by the body and has a connector which is attached to a source of electrical energy. The inner electrode has a washer extending radially outwardly within the inner cavity of the glow plug body. The inner electrode has a frusto-conical wall length extending outwardly on the electrode below the washer. A pressure-applying element is held by the body above the washer and this may be a crimping backup washer against which the body of the glow plug is crimped to hold the assembly together. An insulating ring is held in the inner cavity of the body. The insulating ring has an outer frusto-conical length which meets with the inner cavity of the body, and an inner frusto-conical length which mates with the frusto-conical wall length of the electrode. After the assembly has been assembled under pressure, heat and gas are prevented from leaking through the glow plug by the contact between the four frusto-conical surfaces.